Clinical observations are described in 13 cases of pyomyositis with various cardiovascular complications: (a) pyogenic pericarditis (10 cases) with tamponade in 7 and myopericarditis in 1 case, and (b) acute bacterial endocarditis (3 cases). Blood cultures grew Staphylococcus aureus in all 3 with endocarditis and in 5 of 10 with pericarditis. These complications probably resulted from the bacteraemia which sometimes complicates pyomyositis. Enhanced susceptibility of cardiac muscles to infection in pyomyositis however remains another possibility.